PLOTQUAD integer-variable, x0, y0, x1, y1, x2, y2, x3, y3

Maps a previously loaded sprite onto the quadrilateral defined by four X,Y coordinate pairs.
The first parameter must be an integer variable containing the sprite handle returned by SPRITELOAD. The sprite’s full image is used, positioned by its four destination corners.

example

Key behaviour

Projective mapping: uses a perspective-correct transform (homography), not a simple affine stretch.
Convex quads only: self-intersecting or zero-area quads have undefined results.
Point order: clockwise or anticlockwise is accepted as long as the quad is convex.
Clipping: points may be off-screen; only visible pixels are drawn.
Sprite handle: the first argument must be an integer variable holding a valid handle from SPRITELOAD.

Note: Transparency semantics match PLOT. There is no alpha blending.

Parameters

integer-variable - variable containing a sprite handle from SPRITELOAD.
x0, y0, x1, y1, x2, y2, x3, y3 - integer expressions for the quad’s four destination corners in screen pixels.

Performance notes

Cost is roughly proportional to the quad’s screen area and is naturally slower than PLOT.
There is no Z-buffer. When drawing overlapping quads in one frame, the last drawn appears on top.

Sampling

Uses nearest-neighbour sampling. Large upscales will look blocky; use higher-resolution sprites if you need crisper results.

Examples

REM Upright billboard
PLOTQUAD s, 100,60, 220,60, 220,220, 100,220
 
REM Foreshortened floor tile
PLOTQUAD s, 60,180, 260,180, 220,120, 100,110
 
REM Diamond / 45 degree rotation
PLOTQUAD s, 160,60, 260,140, 160,220, 60,140

See also:
SPRITELOAD · PLOT · SPRITEFREE